Aqueous dispersion and process for production thereof

ABSTRACT

An aqueous dispersion containing a water-insoluble solid, wherein the solid consists of fine particles surfaces of which are coated with a resin having a polyether structure, and a coated amount of the resin is 15 to 1,000 parts by weight per 100 parts of the solid. This aqueous dispersion has improved dispersion stability for various solids such as pigments, dyes, and so on, causes no problems such as precipitation of the solid particles during the storage of the dispersion, and thus can be stably stored for a long time. The present invention can provide an aqueous dispersion used as an ink-jet printing ink, which has good high speed printing properties besides the above properties.

FIELD OF THE INVENTION

The present invention relates to an aqueous dispersion comprising awater-insoluble solid finely dispersed in water, and a method forproducing such a dispersion.

DESCRIPTION OF PRIOR ART

Aqueous dispersions comprising water-insoluble solids finely dispersedin water are widely used as paints, printing inks, liquid developers(wet type toners) and ink-jet printing inks which comprise pigments ordyes as water-insoluble solids; drugs which comprise medicaments aswater-insoluble solids; and industrial products or intermediates whichcomprise catalysts or polymerization initiators as water-insolublesolids.

It is desired for these aqueous dispersions to have good dispersionstability of solid particles and to cause no problem such assedimentation of solid particles during storage so that the dispersionscan be stably stored for a long time. Hitherto, various attempts havebeen made to improve the stability of aqueous dispersions, for example,by selecting particle sizes and dispersion-stabilizers depending on thekinds of solids, or by precipitating a resin having an anionic groupusing an acid on the surfaces of pigment particles as solid particles toform a coating film thereon in the case of ink-jet printing inks(JP-A-9-151342).

However, the above conventional methods may not satisfactorily improvethe dispersion stability and thus the solid particles still precipitateduring storage. Therefore, the deterioration of performance of thedispersion is inevitable or the dispersion cannot be used as intended,when the aqueous dispersion is used in the applications such as paints,printing inks, etc.

DESCRIPTION OF THE INVENTION

One object of the present invention is to provide an aqueous dispersionof solid particles, which can improve the dispersion stability of a widevariety of solid particles such as pigments and dyes, do not cause anyproblem such as precipitation of the solid particles, and can be stablystored for a long time.

Another object of the present invention is to provide an aqueousdispersion which has, in addition to the above characteristics, goodhigh speed-printing properties as an ink-jet printing ink.

As the result of extensive studies by the present inventors to achievethe above objects, it has been found that when a resin having apolyether structure is used as a component for improving the dispersionstability of solid particles in an aqueous medium and an aqueous phaseis mixed with an organic solvent phase containing such a resin and solidparticles, the resin adheres to the surfaces of the solid particles toform fine particles which are coated with the resin, and that the coatedamount of the resin is much larger than the coated amount of a resinwhich is precipitated with an acid as disclosed in JP-A-9-151342 andthereby the dispersion stability of the solid particles is significantlyimproved so that an aqueous dispersion of solid particles, which doesnot have any problem such as precipitation of the particles duringstorage and can be stably stored for a long time, is obtained. This maybe because the resin having the polyether structure is easilyself-dispersed in water. When a pigment is used as solid particles, anaqueous dispersion containing a pigment can be used as an ink-jetprinting ink which does not suffer from the lowering of a surfacetension and has good high speed-printing properties by virtue of theproperties of the resin and the structure of the resin coating.

The present inventions have been completed based on the above findings.

Accordingly, the present invention provides an aqueous dispersioncontaining a water-insoluble solid, wherein the solid consists of fineparticles the surfaces of which are coated with a resin having apolyether structure, and the coated amount of the resin is 15 to 1,000parts by weight per 100 parts of the solid.

Furthermore, the present invention provides a method for producing anaqueous dispersion comprising mixing an organic solvent phase containinga water-insoluble solid and a resin having a polyether structure with anaqueous phase.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The resin having a polyether structure used in the present invention hasa polyester structure which is compatible with the surfaces of the solidparticles and also water and in particular comprises at least one ofpolyoxyethylene and polyoxypropylene structures which have goodhydrophilicity and also a self-dispersing property. That is, when thisresin is dissolved in an organic solvent to form a solution and thesolution is mixed with water, the resin itself is dispersed in water toform a dispersion of finely dispersed resin particles.

To impart such a property to the resin, the resin preferably has a polargroup consisting of an acid or base group in the molecule, inparticular, a carboxyl group, a sulfonic acid group or a phosphonic acidgroup as an acid group. In particular, the resin preferably has acarboxyl group which has a weak acidity so that it less causes thecoagulation of the dispersed particles.

The resin used in the present invention preferably has an acid value of5 to 70 KOH-mg/g, more preferably 10 to 65 KOH-mg/g, most preferably 10to 50 KOH-mg/g. When the acid value of the resin is less than 5 KOH-mg/gor exceeds 70 KOH-mg/g, the resin may be less self-dispersed in themedium. In addition, when the acid value of the resin is too low, theaffinity of the resin with the solid particles decreases so that thefine aqueous dispersion may not be formed or the electric charge on thesolid particles tend to decrease. The fine particles of the solid in theaqueous dispersion preferably have an acid value of 2 to 95 KOH-mg/g,more preferably 5 to 68 KOH-mg/g.

Examples of the resin having the polyether structure include acrylicresins, polyester resins, polyurethane resins, epoxy resins, aminoresins, etc. They may be used independently or as a mixture of two ormore of them. Among them, the acrylic resins, in particular, acrylicresins having the polyether structure in the grafted portions arepreferably used since the introduction of polar groups in the moleculeand grafting are easy, and they can easily attain a self-dispersingproperty in water.

Such an acrylic resin may be prepared by radically polymerizing anacrylic monomer and a monomer having a polar group with a macromonomerhaving a polyether structure and optionally other copolymerizablemonomer in the presence of a polymerization initiator.

Examples of the acrylic monomer include acrylate esters such as methylacrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butylacrylate, tert.-butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate,lauryl acrylate, cetyl acrylate, stearyl acrylate, behenyl acrylate,benzyl acrylate, etc.; and methacrylate esters such as methylmethacrylate, ethyl methacrylate, isopropyl methacrylate, n-propylmethacrylate, n-butyl methacrylate, isobutyl methacrylate, tert.-butylmethacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, laurylmethacrylate, tridecyl methacrylate, cetyl methacrylate, stearylmethacrylate, behenyl methacrylate, benzyl methacrylate, etc. Amongthem, those having a relatively low molecular weight such as methylacrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butylacrylate, tert.-butyl acrylate, methyl methacrylate, ethyl methacrylate,isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate,isobutyl methacrylate, tert.-butyl methacrylate, etc. are particularlypreferable. The amount of such a monomer or monomers is preferably 5 to80% by weight, more preferably 10 to 70% by weight based on the totalweight of the monomers.

As a monomer having a polar group, a monomer having an acid group or amonomer having a base group is used. Examples of the monomer having anacid group include monomers having a carboxyl group such as acrylicacid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylicacid, isopropylacrylic acid, itaconic acid, fumaric acid,acryloyloxyethyl phthalate, acryloyloxy succinate; monomers having asulfonic acid group such as 2-sulfonyletyl acrylate, 2-sulfonylethylmethacrylate, butylarylaminde sulfonic acid, etc.; monomers having aphosphonic acid group such as 2-phosphonylethyl methacrylate,2-phosphonylethyl acrylate, etc.; and monomers having a hydroxyl groupsuch as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,hydroxypropyl acrylate, hydroxypropyl methacrylate, etc. Among them, themonomers having a carboxyl group such as acrylic acid and methacrylicacid, and the monomers having a hydroxyl group such as 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate,hydroxypropyl methacrylate, etc. are particularly preferable.

The amount of the monomer having a carboxyl group is preferably 0.5 to10% by weight, more preferably 1 to 7% by weight based on the totalweight of the monomers. The effects of the present invention are oftenachieved, when the monomer having a hydroxyl group is used in an amountof preferably 10 to 50% by weight, more preferably 20 to 40% by weightbased on the total weight of the monomers.

Examples of the monomer having a base group include monomers having aprimary amino group such as acrylamide, aminoethyl methacrylate,aminopropyl acrylate, methacrylamide, aminoethyl methacrylate,aminopropyl methacrylate, etc.; monomers having a secondary amino groupsuch as methylaminoethyl acrylate, methylaminoproyl acrylate,ethylaminoethyl acrylate, ethylaminopropyl acrylate, methylaminoethylmethacrylate, methylaminopropyl methacrylate, ethylaminoethylmethacrylate, ethylaminopropyl methacrylate, etc.; monomers having atertiary amino group such as dimethylaminoethyl acrylate,diethylaminoethyl acrylate, dimethylaminopropyl methacrylate,diethylaminopropyl acrylate, dimethylaminoethyl methacrylatediethylaminoethyl methacrylate, dimethylaminopropyl methacrylate,diethylaminopropyl methacrylate, etc.; and monomers having a quaternaryammonium group such as dimethylaminoethyl acrylate methyl chloride,dimethylaminoethyl methacrylate methyl chloride, dimethylaminoethylacrylate benzyl chloride, dimethylaminoethyl methacrylate benzylchloride, etc.

Examples of the macromonomer having a polyether structure includemacromonomers comprising methoxy polyethylene glycol or methoxypolypropylene glycol to which an acryloyl group or a methacryloyl groupis bonded directly or via an alkyl group. Preferable examples ofcommercially available macromonomers are PE-200, PE-350, AE-200, AE-350,AP-400, AP-550, AP-800, 70PEP-350B, 10PEP-550B, AEP, SOPOEP-800B,50AOEP-800B, PLE, ALE, PSE, ASE, PNE, ANE, PNP, ANP, PNEP-600, PME-200,PME-400, PME-1000, AME-400, PP-500, PP-800 and PP-100 (all availablefrom NOF Corporation), AMP-10G, AMP-20G, AMP-60G and AM-90G (allavailable from SHIN-NAKAMURA CHEMICAL, Co., Ltd.), BISCOAT #355HP,BISCOAT #310, BISCOAT #310HP, BISCOAT #310HG, BISCOAT #312 and BISCOAT#700 (all available from OSAKA ORGANIC CHEMCAL INDUSTRY LTD.),LIGHT-ACRYLATE EHDG-A, LIGHT-ACRYLATE EC-A, LIGHT-ACRYLATE MTG-A,LIGHT-ACRYLATE 130A, LIGHT-ACRYLATE P-200A, LIGHT-ACRYLATE NP-4EA,LIGHT-ACRYLATE NP-8EA, LIGHT-ESTER MC, LIGHT-ESTER 130MA and LIGHT-ESTER041MA (all available from KYOEISHA CHEMICAL Co., Ltd.), NK ESTER M-20G,NK ESTER M-40G and NK ESTER M-90G (all available from SHIN-NAKAMURACHEMICAL, Co., Ltd.), and ADEKAREASOAP NE-10, ADEKAREASOAP NE-20 andADEKAREASOAP NE-40 (all available from ASAHI DENKA Co., Ltd.).

The macromonomer preferably has a molecular weight of 150 to 10,000,more preferably 180 to 2,000. When the molecular weight of themacromonomer is less than 150, the steric repellency of the graftedgroups decreases when the resin is adhered to the surfaces of the solidparticles so that the particles easily agglomerate, and thus thedispersion may have decreased storage stability. When the molecularweight of the macromonomer exceeds 10,000, the grafted groups causesteric hindrance and the resin has less affinity with the solid, whenthe resin is adhered to the surfaces of the solid particles, and thusthe dispersibility of the particles may deteriorate.

The amount of the macromonomer is preferably 5 to 70% by weight, morepreferably 10 to 50% by weight based on the total weight of themonomers. When the amount of the macromonomer is less than 5% by weight,the effects of the grafted groups decrease so that the resin has lowerself-dispersing property. When the amount of the macromonomer exceeds70% by weight, the hydrophilicity of the resin increases so that theresin is easily dissolved in water and the resin tends to hardly adhereto the surfaces of the solid particles.

Examples of the other copolymerizable monomer include styrenic monomerssuch as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene,p-methylstyrene, p-tert.-butylstyrene, etc.; itaconates such as benzylitaconate; maleates such as dimethyl maleate, etc.; fumarates such asdimethyl fumarate, etc.; α-olefins such as ethylene, etc.;acrylonitrile, methacrylonitrile, vinyl acetate, glycidyl methacrylate,glycidyl acrylate, and so on. Among them, styrenic monomers such asstyrene, α-methylstyrene, o-methylstyrene, m-methylstyrene,p-methylstyrene, etc. or glycidyl group-containing monomers such asglycidyl methacrylate, glycidyl acrylate, etc. are particularlypreferable. The amount of the styrenic monomer is preferably 5 to 50% byweight, more preferably 10 to 30% by weight based on the total weight ofthe monomers. The effects of the present invention are often achievedwhen the glycidyl group-containing monomer is preferably used in anamount of 1 to 15% by weight, more preferably 2 to 10% by weight basedon the total weight of the monomers.

The radial polymerization may be carried out by any conventionalpolymerization process, for example, bulk polymerization, solutionpolymerization, suspension polymerization, emulsion polymerization, andredox polymerization. The solution polymerization is preferable sincethe reaction mode is simple. Examples of unreactive solvents used forthe solution polymerization include aliphatic hydrocarbons such ashexane, mineral spirits, etc.; aromatic hydrocarbons such as benzene,toluene, xylene, etc.; esters such as butyl acetate, etc.; alcohols suchas methanol, butanol, etc.; ketones such as methyl ethyl ketone,isobutyl methyl ketone, etc.; and aprotic polar solvents such asdimethylformamide, dimethlsulfoxide, N-methylpyrrolidone, pyridine, etc.Optionally, these solvents may be used in admixture.

The radical polymerization initiator may be any conventionalpolymerization initiator, and examples thereof include organic peroxidessuch as tert.-butyl peroxybenzoate, di-tert.-butyl peroxide, cumeneperhydroxide, acetyi peroxide, benzoyl peroxide, lauroyl peroxide, etc.;azo compounds such as azobisbutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexane carbonitrile, etc.

Reaction conditions in the radial polymerization vary depending on thekind of the polymerization initiator, the kind of the solvent, and soon. A reaction temperature is usually 180° C. or less, preferably 30 to150° C., and a reaction time is usually 0.5 to 40 hours, preferably 2 to30 hours.

The resin having the polyether structure used in the present inventionpreferably has a number average molecular weight of 1,000 to 100,000,more preferably 3,000 to 30,000. When the number average molecularweight of the resin is less than 1,000, it may be difficult to finelydisperse the solid particles in water and the solid particles tend toprecipitate. When the number average molecular weight of the resinexceeds 100,000, the resin may hardly be dissolved in the solvent andthus the viscosity of the aqueous dispersion tends to greatly increase.

The water-insoluble solids used in the present invention may beinorganic pigments, organic pigments, dyes which are insoluble in waterand organic solvents, in the case of paints, printing inks, inparticular, ink-jet printing inks, liquid developers, and so on.Besides, various solid materials insoluble in water and organic solventssuch as fillers, medicaments, polymerization initiators, catalysts, UVabsorbers, etc. may be used depending on the applications of thedispersions.

Examples of the inorganic pigment include titanium oxide, Chinese white,zinc oxide, lithopone, iron oxide, aluminum oxide, silicon dioxide,kaolinite, montmorillonite, talc, barium sulfate, calcium carbonate,silica, alumina, cadmium red, colcothar, molybdenum red, chromevermilion, molybdate orange, chrome yellow, cadmium yellow, iron oxideyellow, titanium yellow, chromium oxide, blue green, cobalt green,titanium-cobalt green, cobalt-chrome green, ultramarine, ultramarineblue, dark blue, cobalt blue, cerulean blue, manganese violet, cobaltviolet, mica, etc.

Preferable examples of the organic pigment include azo pigments,azomethine pigments, polyazo pigments, phthalocyanine pigments,quinacridone pigments, anthraquinone pigments, indigo pigments,thioindigo pigments, quinophthalone pigments, benzimidazolone pigments,isoindoline pigments, isoindolinone pigments, or carbon black includingacidic, neutral or basic carbon black, etc. Examples of the dye which isinsoluble in water or organic solvents include azo dyes, anthraquinonedyes, indigo dyes, phthalocyanine dyes, carbonyl dyes, quinoneiminedyes, methine dyes, quinoline dyes, nitro dyes, etc. Among them,disperse dyes are preferable. In particular, pigments are preferablefrom the viewpoint of water and weather resistances.

Specific examples of a pigment which is used in a cyan ink compositioninclude C.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22, 60, etc.Among them, C.I. Pigment Blue 15:3 and 15:4 or their mixtures arepreferable.

Specific examples of a pigment which is used in a magenta inkcomposition include C.I. Pigment Red 5, 7, 12, 48(Ca), 49(Mn), 57 (Ca),57:1, 112, 122, 123, 168, 184, 202 and 209, and C.I. Pigment Violet 19,etc. Among them, C.I. Pigment Red 57:1, 122, 202 and 209, and C.I.Pigment Violet 19 and their mixtures are preferable.

Specific examples of a pigment which is used in a yellow ink compositioninclude C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83,93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 130, 138, 150, 151, 154,155, 180 and 185. Among them, C.I. Pigment Yellow 14, 74, 83, 109, 110,120, 150, 151, 155 and 180 and their mixtures are preferable.

Specific examples of a pigment which is used in a black ink compositioninclude HCF, MCF, RCF, LFF and SCF (all available form MitsubishiChemical Corporation), Monarch and Regal (both available from CabotCorporation), Color Black, Special Black and Printex (all available fromDegussa-Huls AG), TOKA Black (available from Tokai Carbon Co., Ltd.),Raven (available from Columbian Chemicals Co.), and so on. Inparticular, HCF #2650, # 2600 # 2350 and #2300, MCF #1000, #980, #970and #960, MCF 88, LFFMA 7, MA 8, MA 11, MA 77 and MA 100 (all availableform Mitsubishi Chemical Corporation), Printex 95, 85, 75, 55, 45 and 25(all available from Degussa-Huls AG) and their mixtures are preferablyused.

In the present invention, the amount of the resin to be coated on thesolid particles is usually 15 to 1,000 parts by weight, preferable 20 to500 parts by weight, more preferably 25 to 200 parts by weight, per 100parts by weight of the solid. The fine particles of the solid have anaverage particle size of 0.01 to 0.3 μm, more preferably 0.015 to 0.2μm.

The coated structure of the solid particles with the resin is based onthe bonding between the resin and the solid particles via chemical bondsbetween the resin and the solid (acid-base bonds, ionic bonds, covalentbonds, etc.), physical bonds (bonding formed by resin aggregation,mechanical bonds through dispersion force, etc.), physicochemical bonds,or any combination of these bonds. These bonds provide fairly strongadhesion states. The coated amount of the resin may be indirectlymeasured by adjusting a concentration of nonvolatiles in the aqueousdispersion to 2% by weight, subjecting the aqueous dispersion tocentrifugation until a supernatant becomes transparent, and thenmeasuring a resin concentration in the supernatant.

Besides the properties described above, the aqueous dispersion of thepresent invention has a far better dispersion stability thanconventional aqueous dispersions containing a water-insoluble solid,since the solid particles have the coating structure as described above,and in particular, the coated amount of the resin is high, and thereforethe solid particles are stably dispersed in water in the form of fineparticles as describe above. As a result, the aqueous dispersion of thepresent invention does not suffer from problems such as precipitationduring storage and it can be stably stored for a long time.

In contrast, when the coated amount of the resin and/or the averageparticle size of the coated solid particles are outside the determinedranges, the above effects are hardly attained. In particular, when thecoated amount of the resin is less than 15 parts by weight per 100 partsby weight of the solid, the solid particles tend to agglomerate togetherso that the storage stability of the dispersion decreases, and thefixing of the solid particle onto a printing substrate deteriorates.When the coated amount of the resin exceeds 1,000 parts by weight, theabove effects may saturate. When the average particle size of the fineparticles exceeds 0.3 μm, the dispersion stability tends to decrease andthus the solid particles may agglomerate. When the dispersion containingsolid particles having such a large average particle size is formulatedas an ink, color reproducibility of a printed material may deteriorate,or a nozzle of an ink-jet printer may be clogged with the particles.When the fine particles have an average particle size of less than 0.01μm, the contrast of a printed material may decrease.

In addition to the dispersion stability, the aqueous dispersion of thepresent invention can maintain a high surface tension since the resinhas the above properties and the coating structure. The surface tensionof the dispersion is 3.0×10⁻⁴ to 6.0×10⁻⁴ N/cm, preferably 3.5×10⁻⁴ to5.5×10 N/cm, at a solid concentration of 3 to 10% by weight.Consequently, when the aqueous dispersion is used as an ink-jet printingink, droplets of the dispersion form stale spheres and thus, an imageprinted is not distorted, and the aqueous dispersion has excellent highspeed printing properties.

When an aqueous dispersion having a surface tension of less than3.0×10⁻⁴ N/cm is used as an ink-jet printing ink, the droplet of thedispersion does not form a stable spherical shape so that the printedimage may be distorted and the high speed printing property may beimpaired.

JP-A-10-279873 proposes the use of a resin containing a siliconecomponent as a dispersion stabilizer to improve the storage stability ofan ink. However, the ink has a surface tension of less than 3.0×10⁻⁴N/cm, and it cannot satisfy the properties of an ink-jet printing inksuch as a high speed printing property.

The aqueous dispersion of the present invention may be prepared bymixing the organic phase containing the water-insoluble solid and theresin having a polyether structure with an aqueous phase and adheringthe resin onto the surfaces of the solid particles to form fineparticles the surfaces of which are coated with the resin. In thisprocess, the large amount of the resin is easily deposited and adheredonto the surfaces of the solid particles, and thus the coated structureof the solid particles having a coated amount of 15% by weight or morebased on the weight of the solid can be formed.

In a specific embodiment of the present invention, the above process canbe carried out by the following steps:

A) dispersing the water-insoluble solid in an organic solvent in whichthe resin having the polyether structure has been dissolved;

B) pouring water in the dispersion prepared in the previous step, orpouring the dispersion prepared in the previous step in water, andmixing the dispersion and water to deposit and adhere the resin to thesurfaces of the solid particles; and

C) if necessary, evaporating off the solvent to concentrate thedispersion after the previous mixing step.

In step A, the resin having the polyether structure is dissolved in anorganic solvent and then the water-insoluble solid is added to thesolution. Thereafter, the mixture is dispersed with a dispersingapparatus such as a bead mill (e.g. DYNO Mill, DSP Mill, etc.), a rollmill, a sand mill, an atriter, a kneader, a high pressure jet mill (e.g.a nanomizer etc.) and the like, optionally using a dispersing mediumsuch as glass beads, steal beads, zircona beads, etc. In the dispersingstep, various additives such as a surfactant, other resin, a pigmentdisperser, a pigment derivative, a charge generator, etc. may be addedto the dispersion.

Conditions for dispersing the solid in the medium depend on the kind ofthe solid, the type of the dispersing apparatus, and so on. In view ofeconomical production of the dispersion, a temperature is in a range of0 to 150° C., and a dispersing time is as short as possible. Adispersing time of 0.1 to 10 hr/kg is satisfactory from the viewpoint ofproductivity.

The particle size after dispersing is suitably selected so that theaverage particle size of the intended solid particles coated with theresin is within the above-described range. A method for measuring aparticle size is not limited and any conventional method may be used.For example, a particle size may be measured with a particle sizemeasuring apparatus of a laser scattering type or a centrifugalsedimentation type.

In step B, water is slowly added to and mixed with the dispersionprepared in step A, or vice versa. In this case, during or afteraddition, the mixture is uniformly mixed with a simple stirringapparatus such as a Three-One Motor, a magnetic stirrer, a Disper, ahomogenizer, etc. A mixer such as a line mixer may also be used.Furthermore, to finely divide the precipitated particles, a dispersingapparatus such as a bead mill or a high pressure jet mill may be used.

Step C is carried out to remove an organic solvent, when the presence ofthe organic solvent in the dispersion is not desired. For concentration,a conventional distillation method under atmospheric or reduced pressuremay be employed. The organic solvent to be removed in the concentrationstep is one that is used in step A for dissolving the resin having thepolyether structure. Preferably, such a solvent is an organic solventwhich is easily soluble in water and has a boiling point of 100° C. orlower, for example, methyl ethyl ketone, tetrahydrofuran, isopropanol,ethanol, etc.

The aqueous dispersion prepared by the above method usually containswater in an amount of 50 to 10,000 parts by weight, preferably 100 to3,000 parts by weight, per 100 parts by weight of the water-insolublesolid.

The aqueous dispersion of the present invention may optionally containvarious additives which are added to the dispersion during thepreparation thereof if necessary, for example, a surfactant, a pigmentdisperser, a pigment derivative, a charge generator, and further apreservative, a deodorant, an anti-skinning agent, a perfume, etc.

The aqueous dispersion of the present invention having the abovecomposition can be used in various applications depending on the kind ofthe solid contained. When the pigment is used as the solid, the aqueousdispersion is useful as a paint, a printing ink such as a gravure ink,an ink-jet printing ink, a liquid toner for a wet typeelectrophotographic printer or an ink-jet printer using electrostaticforce. In particular, in the field of inks, the aqueous dispersion ofthe present invention can be stably used for a long time since thesurfaces of the pigment particles are coated with the resin having thepolyether structure which can be self-dispersed in water and thus theyare hardly agglomerated.

When the aqueous dispersion of the present invention is used in each ofthe above applications, a binder and/or an organic solvent are added,and various additives are added to the dispersion in accordance with theapplication to adjust a solid content or a binder concentration. In thiscase, the mixture of the dispersion and the binder, organic solventand/or additives may be mixed with a simple stirring apparatus such as aDisper, and any conventionally used dispersing apparatus is notnecessary. Therefore, the aqueous dispersion of the present inventioncan contribute to energy saving and cost reduction.

The binder may be any resin that is conventionally used as a binder.Examples of such resins include natural proteins, celluloses, andsynthetic polymers such as polyvinyl alcohol, polyacrylamide,polyacrylic acid, polyvinyl ether, polyvinylpyrrolidone, acrylic resins,polyester resins, alkyd resins, polyurethane resins, polyamide resins,aromatic polyamide resins, melamine resins, polyether resins,fluororesins, styrene-acryl resins, styrene-maleic acid resins, etc., aswell as photosensitive resins, thermosetting resins, UV curable resinsand electron beam curable resins.

Examples of the additives above include anionic, cationic and nonionicsurfactants, an anti-skinning agent, a leveling agent, a metal soap, acharge-adjusting agent such as lecithin, a wetting agent, and so on.

EXAMPLES

The present invention will be illustrated by the following examples.

In the examples, “parts” and “%” are “parts by weight” and “% by weight”unless otherwise indicated. Reagents which are not specifically notedare all Fist Grade chemicals available from WAKO Pure ChemicalIndustries, Ltd.

Self-Dispersible Polymers A to G used in the Examples below as resinshaving a polyether structure, which are self-dispersed in water, weresynthesized in following Synthesis Examples 1 to 7.

Polymer H having no polyether structure, and Polymer I having apolyether structure and an acid value exceeding 70 KOH-mg/g, which wereused in Comparative Examples instead of the self-dispersible polymers,were synthesized in Comparative Synthesis Examples 1 and 2,respectively.

Synthesis Example 1

Synthesis of Self-Dispersible Polymer A n-Butyl acrylate 33.3 partsn-Butyl methacrylate 10.9 parts Styrene 20.0 parts Methacrylic acid  4.5parts Glycidyl methacrylate  4.5 parts PME-400 26.7 parts (Methoxypolyethylene glycol monomethacrylate available from NOF Corp.) PerbutylO  4.0 parts (Peroxy ester available from NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 75° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 4 hours, and thereafter furtherreacted at 75° C. for 5 hours. The solution after reaction had annonvolatile content of 51.0% and an acid value of 29.0 KOH-mg/g, andcontained Polymer A having a number average molecular weight of 13,000.

One part of Polymer A was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer A. Polymer A wasself-dispersed to obtain a dispersion having an average particle size of0.035 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Synthesis Example 2

Synthesis of Self-Dispersible Polymer B n-Butyl acrylate 33.3 partsn-Butyl methacrylate 10.9 parts Styrene 20.0 parts Methacrylic acid  4.5parts Glycidyl methacrylate  4.5 parts AME-400 26.7 parts (Methoxypolyethylene glycol monoacrylate available from NOF Corp.)2,2-Azobisisobutyronitrile  4.0 parts

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 75° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 4 hours, and thereafter furtherreacted at 75° C. for 5 hours. The solution after reaction had annonvolatile content of 51.5% and an acid value of 27.5 KOH-mg/g, andcontained Polymer B having a number average molecular weight of 7,000.

One part of Polymer B was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer B. Polymer B wasself-dispersed to obtain a dispersion having an average particle size of0.032 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Synthesis Example 3

Synthesis of Self-Dispersible Polymer C n-Butyl acrylate 23.3 partsn-Butyl methacrylate  9.6 parts Styrene 20.0 parts Methacrylic acid  3.0parts Glycidyl methacrylate  7.5 parts PME-400 26.6 parts (Methoxypolyethylene glycol monomethacrylate available from NOF Corp.) AMP-10G10.0 parts (Phenoxyethyl acrylate available from Shin-Nakamura Chemical,Co. Ltd.) 2,2-Azobisisobutyronitrile  4.0 parts

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 75° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 4 hours, and thereafter furtherreacted at 75° C. for 5 hours. The solution after reaction had annonvolatile content of 44.7% and an acid value of 19.7 KOH-mg/g, andcontained Polymer C having a number average molecular weight of 13,000.

One part of Polymer C was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer C. Polymer C wasself-dispersed to obtain a dispersion having an average particle size of0.040 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Synthesis Example 4

Synthesis of Self-Dispersible Polymer D n-Butyl acrylate 30.0 partsn-Butyl methacrylate 26.0 parts Styrene  6.7 parts Methacrylic acid  4.0parts PME-1000 33.3 parts (Methoxy polyethylene glycol monomethacrylateavailable from NOF Corp.) Perbutyl O  2.0 parts (Peroxy ester availablefrom NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 80° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 2 hours, and thereafter furtherreacted at 80° C. for 13 hours. The solution after reaction had annonvolatile content of 50.5% and an acid value of 26.2 KOH-mg/g, andcontained Polymer D having a number average molecular weight of 21,000.

One part of Polymer D was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer D. Polymer D wasself-dispersed to obtain a dispersion having an average particle size of0.045 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Synthesis Example 5

Synthesis of Self-Dispersible Polymer E n-Butyl acrylate 15.5 partsStyrene 20.0 parts NK ESTER SA 25.0 parts (β-Methacryloyloxyethylhydrogen succinate available from Shin-Nakamura Chemical Co., Ltd.)Glycidyl methacrylate  7.5 parts PME-400 32.0 parts (Methoxypolyethylene glycol monomethacrylate available from NOF Corp.) PerbutylO  4.0 parts (Peroxy ester available from NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 75° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 4 hours, and thereafter furtherreacted at 75° C. for 5 hours. The solution after reaction had annonvolatile content of 47.3% and an acid value of 45.6 KOH-mg/g, andcontained Polymer E having a number average molecular weight of 16,000.

One part of Polymer E was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer E. Polymer E wasself-dispersed to obtain a dispersion having an average particle size of0.025 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Synthesis Example 6

Synthesis of Self-Dispersible Polymer F n-Butyl methacrylate 14.9 partsStyrene 20.0 parts Methacrylic acid  5.0 parts 2-Hydroxyethylmethacrylate 33.3 parts Glycidyl methacrylate  5.6 parts PP-500 21.2parts (Polypropylene glycol monomethacrylate available from NOF Corp.)Perbutyl O  6.0 parts (Peroxy ester available from NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 75° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 4 hours, and thereafter furtherreacted at 75° C. for 5 hours. The solution after reaction had annonvolatile content of 47.7% and an acid value of 34.5 KOH-mg/g, andcontained Polymer F having a number average molecular weight of 10,000.

One part of Polymer F was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer F. Polymer F wasself-dispersed to obtain a dispersion having an average particle size of0.055 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Synthesis Example 7

Synthesis of Self-Dispersible Polymer G n-Butyl methacrylate 44.3 partsMethacrylic acid  1.5 parts Glycidyl methacrylate  7.5 parts AMP-10G20.0 parts (Phenoxyethyl acrylate available from Shin-Nakamura Chemical,Co. Ltd.) PP-800 26.7 parts (Polypropylene glycol monomethacrylateavailable from NOF Corp.) Perbutyl O  4.0 parts (Peroxy ester availablefrom NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 75° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 4 hours, and thereafter furtherreacted at 75° C. for 5 hours. The solution after reaction had annonvolatile content of 48.8% and an acid value of 14.6 KOH-mg/g, andcontained Polymer G having a number average molecular weight of 15,000.

One part of Polymer G was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer G. Polymer G wasself-dispersed to obtain a dispersion having an average particle size of0.098 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.).

Comparative Synthesis Example 1

Synthesis of Polymer H having no polyether structure n-Butyl acrylate41.3 parts n-Butyl methacrylate 23.0 parts Styrene 17.2 partsMethacrylic acid  3.5 parts 2-Hydroxyethyl methacrylate 15.0 partsPerbutyl O  2.0 parts (Peroxy ester available from NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 80° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 2 hours, and thereafter furtherreacted at 80° C. for 15 hours. The solution after reaction had annonvolatile content of 52.0% and an acid value of 25.8 KOH-mg/g, andcontained Polymer H having a number average molecular weight of 24,000.

One part of Polymer H was diluted with methyl ethyl ketone, and then 0.5part of water was added to dilute Polymer H. However, Polymer H was notself-dispersed, but it was precipitated. That is, Polymer H had noproperty to be self-dispersed in water since it had no polyetherstructure in the molecule.

Comparative Synthesis Example 2

Synthesis of polymer having a polyether structure and an acid valueexceeding 70 KOH-mg/g n-Butyl acrylate 22.9 parts n-Butyl methacrylate10.9 parts Styrene 20.0 parts Methacrylic acid 15.0 parts Glycidylmethacrylate  4.5 parts PME-400 26.7 parts (Methoxy polyethylene glycolmonomethacrylate available from NOF Corp.) Perbutyl O  4.0 parts (Peroxyester available from NOF Corp.)

The above ingredients were mixed to form a solution.

In a reactor equipped with a nitrogen gas inlet tube, methyl ethylketone (100 parts) was charged and heated up to 80° C. while introducingnitrogen gas in the reactor. To methyl ethyl ketone in the reactor, theabove solution was dropwise added over 2 hours, and thereafter furtherreacted at 80° C. for 12 hours. The solution after reaction had annonvolatile content of 51.3% and an acid value of 71.8 KOH-mg/g, andcontained Polymer I having a number average molecular weight of 14,000.

One part of Polymer I was diluted with methyl ethyl ketone, and then 2parts of water was added to dilute Polymer I. Polymer I wasself-dispersed to obtain a dispersion having an average particle size of0.015 μm (measured with a laser Doppler type particle size distributionmeter “N4 PLUS” manufactured by Beckman Coulter, Inc.), but it was foundthat a part of Polymer I was dissolved in water.

Example 1

In a 100 cc plastic bottle, 4.0 parts of Self-Dispersible Polymer Aprepared in Synthesis Example 1, 4.0 parts of copper phthalocyanine bluepigment (FASTGEN BLUE GNPS available from Dainippon Ink and ChemicalsInc.) as a solid, 12.0 parts of methyl ethyl ketone and 100 parts ofzirconia beads having a diameter of 3 mm were weighed and charged, andthen the mixture was dispersed with a paint shaker (available from ToyoSeiki Kogyo Co., Ltd.) for 2 hours. Thereafter, 10.0 parts of methylethyl ketone was further added to the mixture to obtain a dispersion ina slurry form.

Then, 0.2 part of 2-dimethylaminoethanol and 44.8 parts of water werecharged in a beaker and stirred with a magnetic stirrer. To thismixture, 15.0 parts of the above dispersion was slowly dropwise addedwhile stirring to obtain fine particles of the pigment, to the surfacesof which Polymer A was deposited and adhered. After that, methyl ethylketone was evaporated off under reduced pressure to obtain an aqueousdispersion having a pigment concentration of 4.65%.

This aqueous dispersion had an average particle size of 0.156 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.9×10⁻⁴ N/cm, and a viscosity of 1.49 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 31.5 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.158 μm, a surfacetension of 3.9×10⁻⁴ N/cm, and a viscosity of 1.47 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 63.2 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and24.5 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.155 μm, a surface tension of3.3×10⁻⁴ N/cm and a viscosity of 1.36 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.158 μm, a surface tension of 3.2×10⁻⁴ N/cm, and aviscosity of 1.34 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 2

An aqueous dispersion having a pigment concentration of 4.60% wasprepared in the same manner as in Example 1 except that 4.0 parts of aquinacridone pigment (CINQUASIA MAGENTA RT-355-D available from CibaSpecialty Chemicals) was used in place of 4.0 parts of copperphthalocyanine blue pigment (FASTGEN BLUE GNPS available from DainipponInk and Chemicals Inc.)

This aqueous dispersion had an average particle size of 0.158 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.6×10⁻⁴ N/cm, and a viscosity of 1.48 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 25.5 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.158 μm, a surfacetension of 3.6×10⁻⁴ N/cm, and a viscosity of 1.47 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 65.2 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and22.8 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.152 μm, a surface tension of3.2×10⁻⁴ N/cm and a viscosity of 1.89 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.151 μm, a surface tension of 3.2×10⁻⁴ N/cm, and aviscosity of 1.86 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 3

An aqueous dispersion having a pigment concentration of 4.96% wasprepared in the same manner as in Example 1 except that 4.0 parts ofSelf-Dispersible Polymer B prepared in Synthesis Example 2 was used inplace of 4.0 parts of Self-Dispersible Polymer A prepared in SynthesisExample 1.

This aqueous dispersion had an average particle size of 0.126 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of4.3×10⁻⁴ N/cm, and a viscosity of 1.38 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 38.6 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.130 μm, a surfacetension of 4.3×10⁻⁴ N/cm, and a viscosity of 1.37 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 60.5 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and27.5 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.133 μm, a surface tension of3.7×10⁻⁴ N/cm and a viscosity of 1.31 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.134 μm, a surface tension of 3.6×10⁻⁴ N/cm, and aviscosity of 1.30 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 4

An aqueous dispersion having a pigment concentration of 5.98% wasprepared in the same manner as in Example 1 except that 4.0 parts ofcarbon black (Printex 85 available from Degussa-Huls AG) was used inplace of 4.0 parts of copper phthalocyanine blue pigment (FASTGEN BLUEGNPS available from Dainippon Ink and Chemicals Inc.), and 4.0 parts ofSelf-Dispersible Polymer C prepared in Synthesis Example 3 was used inplace of 4.0 parts of Self-Dispersible Polymer A prepared in SynthesisExample 1.

This aqueous dispersion had an average particle size of 0.149 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of4.1×10⁻⁴ N/cm, and a viscosity of 1.89 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 44.3 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.146 μm, a surfacetension of 4.1×10⁻⁴ N/cm, and a viscosity of 1.91 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 83.6 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and4.4 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 5%.

This ink had an average particle size of 0.149 μm, a surface tension of3.7×10⁻⁴ N/cm and a viscosity of 1.76 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.150 μm, a surface tension of 3.6×1 0⁻⁴ N/cm, and aviscosity of 1.77 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 5

An aqueous dispersion having a pigment concentration of 6.30% wasprepared in the same manner as in Example 1 except that 4.0 parts ofSelf-Dispersible Polymer D prepared in Synthesis Example 4 was used inplace of 4.0 parts of Self-Dispersible Polymer A prepared in SynthesisExample 1.

This aqueous dispersion had an average particle size of 0.157 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.4×10⁻⁴ N/cm, and a viscosity of 1.99 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 33.5 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.156 μm, a surfacetension of 3.4×04 N/cm, and a viscosity of 1.97 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 47.6 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and40.4 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.156 μm, a surface tension of3.0×10⁻⁴ N/cm and a viscosity of 1.73 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.158 μm, a surface tension of 3.0×10⁻⁴ N/cm, and aviscosity of 1.78 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 6

An aqueous dispersion having a pigment concentration of 4.30% wasprepared in the same manner as in Example 1 except that 4.0 parts ofSelf-Dispersible Polymer E prepared in Synthesis Example 5 was used inplace of 4.0 parts of Self-Dispersible Polymer A prepared in SynthesisExample 1.

This aqueous dispersion had an average particle size of 0.142 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.8×10⁻⁴ N/cm, and a viscosity of 2.00 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 43.5 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.146 μm, a surfacetension of 3.8×10⁻⁴ N/cm, and a viscosity of 1.97 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 69.8 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and18.2 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.145 μm, a surface tension of3.3×10⁻⁴ N/cm and a viscosity of 1.78 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.149 μm, a surface tension of 3.3×10⁻⁴ N/cm, and aviscosity of 1.80 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 7

An aqueous dispersion having a pigment concentration of 5.08% wasprepared in the same manner as in Example 1 except that 4.0 parts of adisazo pigment (Yellow HGAF LP901 available from Clariant Corp.) wasused in place of 4.0 parts of copper phthalocyanine blue pigment(FASTGEN BLUE GNPS available from Dainippon Ink and Chemicals Inc.), theamount of methyl ethyl ketone was reduced from 12.0 parts to 10.0 parts,and 2.0 parts of n-hexane was added.

This aqueous dispersion had an average particle size of 0.189 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.6×10⁻⁴ N/cm, and a viscosity of 1.66 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 26.5 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.146 μm, a surfacetension of 3.7×10⁻⁴ N/cm, and a viscosity of 1.63 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 59.0 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and29.0 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.190 μm, a surface tension of3.3×10⁻⁴ N/cm and a viscosity of 1.58 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.192 μm, a surface tension of 3.2×10⁻⁴ N/cm, and aviscosity of 1.57 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 8

An aqueous dispersion having a pigment concentration of 4.63% wasprepared in the same manner as in Example 1 except that 4.0 parts ofSelf-Dispersible Polymer F prepared in Synthesis Example 6 was used inplace of 4.0 parts of Self-Dispersible Polymer A prepared in SynthesisExample 1.

This aqueous dispersion had an average particle size of 0.190 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of 3.5×1N/cm, and a viscosity of 1.89 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 32.2 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.188 μm, a surfacetension of 3.5×10⁻⁴ N/cm, and a viscosity of 1.88 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 64.8 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and23.2 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.195 μm, a surface tension of3.2×10⁻⁴ N/cm and a viscosity of 1.67 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.193 μm, a surface tension of 3.1×10⁻⁴ N/cm, and aviscosity of 1.68 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Example 9

An aqueous dispersion having a pigment concentration of 4.30% wasprepared in the same manner as in Example 1 except that 4.0 parts ofSelf-Dispersible Polymer G prepared in Synthesis Example 7 was used inplace of 4.0 parts of Self-Dispersible Polymer A prepared in SynthesisExample 1.

This aqueous dispersion had an average particle size of 0.135 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.8×10⁻⁴ N/cm, and a viscosity of 1.76 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 36.9 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.138 μm, a surfacetension of 3.8×10⁻⁴ N/cm, and a viscosity of 1.78 mPa·s. These resultsshow that the pigment particles did not agglomerate in the above storagetest, and the aqueous dispersion had excellent storage stability.

To 69.8 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and18.2 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.138 μm, a surface tension of3.3×10⁻⁴ N/cm and a viscosity of 1.82 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.141 μm, a surface tension of 3.3×10⁻⁴ N/cm, and aviscosity of 1.80 mPa·s. These results show that the pigment particlesin the ink did not agglomerate in the above storage test, and the inkhad excellent storage stability.

Comparative Example 1

In a 100 cc plastic bottle, 20.0 parts of a styrene-acrylic resin(JOHNCRYL available from Johnson Polymer) as a non-self-dispersiblepolymer, 20.0 parts of copper phthalocyanine blue pigment (FASTGEN BLUEGNPS available from Dainippon Ink and Chemicals Inc.) as a solid, 57.0parts of water, 1.8 parts of an antifoaming agent (SURFINOL 104available from Nissin Chemical Industries, Ltd.) and 100 parts ofzirconia beads having a diameter of 3 mm were weighed and charged, andthen the mixture was dispersed with a paint shaker (available from ToyoSeiki Kogyo Co., Ltd.) for 2 hours. Thereafter, 253.0 parts of water and46.5 parts of the same styrene-acrylic resin as above (JOHNCRYLavailable from Johnson Polymer) were further added to the mixture toobtain an aqueous dispersion having a pigment concentration of 5.00%.

This aqueous dispersion had an average particle size of 0.179 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.2×10⁻⁴ N/cm, and a viscosity of 1.97 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was 2.3 parts per 100 parts of the pigment. This resultmeans that the above resin hardly adhered to the pigment particlesurfaces.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 3 days. Thereafter,the dispersion had an average particle size of 0.335 μm, a surfacetension of 2.9×10⁻⁴ N/cm, and a viscosity of 4.26 mPa·s. Accordingly,the pigment particles agglomerated and slightly precipitated in theabove storage test, and the aqueous dispersion lacked storage stability.

To 60.0 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and28.0 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.169 μm, a surface tension of2.8×10⁻⁴ N/cm and a viscosity of 1.89 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 3 days. Thereafter, the ink had an averageparticle size of 0.648 μm, a surface tension of 2.8×10⁻⁴ N/cm, and aviscosity of 4.75 mPa·s. These results show that the pigment particlesin the ink agglomerates in the above storage test, and the ink lackedstorage stability.

Comparative Example 2

An aqueous dispersion having a pigment concentration of 4.86% wasprepared in the same manner as in Example 1 except that 4.0 parts ofPolymer H having no polyether structure prepared in ComparativeSynthesis Example 1 was used in place of 4.0 parts of Self-DispersiblePolymer A prepared in Synthesis Example 1.

This aqueous dispersion had an average particle size of 0.360 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.1×10⁻⁴ N/cm, and a viscosity of 2.09 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was only 11.2 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.538 μm, a surfacetension of 2.8×10⁴ N/cm, and a viscosity of 5.78 mPa·s. Accordingly, thepigment particles agglomerated in the above storage test, and theaqueous dispersion lacked storage stability.

To 61.7 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and26.3 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.455 μm, a surface tension of2.6×10⁻⁴ N/cm and a viscosity of 3.68 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.523 μm, a surface tension of 2.5×10⁻⁴ N/cm, and aviscosity of 4.08 mPa·s. These results show that the pigment particlesin the ink agglomerates and slightly precipitated in the above storagetest, and the ink lacked storage stability.

Comparative Example 3

An aqueous dispersion having a pigment concentration of 5.19% wasprepared in the same manner as in Example 1 except that 4.0 parts ofPolymer I having a polyether structure and an acid value exceeding 70KOH-mg/g prepared in Comparative Synthesis Example 2 was used in placeof 4.0 parts of Self-Dispersible Polymer A prepared in Synthesis Example1.

This aqueous dispersion had an average particle size of 0.230 μm(measured with a laser Doppler type particle size distribution meter “N4PLUS” manufactured by Beckman Coulter, Inc.), a surface tension of3.2×10⁻⁴ N/cm, and a viscosity of 2.87 mPa·s.

The nonvolatile concentration of the aqueous dispersion was adjusted at2% with water, and the dispersion was subjected to centrifugation of33,500 G for 5 hours. Then, a coated amount of the resin was calculatedfrom the amount of nonvolatiles in the supernatant. The amount of theresin coated was only 10.4 parts per 100 parts of the pigment.

Furthermore, the aqueous dispersion was subjected to a storage test bystoring it in a thermostatic chamber at 70° C. for 14 days. Thereafter,the dispersion had an average particle size of 0.453 μm, a surfacetension of 2.7×10⁻⁴ N/cm, and a viscosity of 4.34 mPa·s. Accordingly,the pigment particles agglomerated in the above storage test, and theaqueous dispersion lacked storage stability.

To 57.8 parts of the aqueous dispersion, 10.0 parts of triethyleneglycol mono-n-butyl ether as a penetrant, 2.0 parts of an antifoamingagent (SURFINOL 465 available from Nissin Chemical Industries, Ltd.) and30.2 parts of water were added to obtain an aqueous ink-jet printing inkhaving a pigment content of 3%.

This ink had an average particle size of 0.280 μm, a surface tension of2.8×10⁻⁴ N/cm and a viscosity of 2.88 mPa·s.

The ink was subjected to a storage test by storing it in a thermostaticchamber at 70° C. for 14 days. Thereafter, the ink had an averageparticle size of 0.368 μm, a surface tension of 2.6×10⁻⁴ N/cm, and aviscosity of 3.38 mPa·s. These results show that the pigment particlesin the ink agglomerates and slightly precipitated in the above storagetest, and the ink lacked storage stability.

EFFECTS OF THE INVENTION

As described above, the present invention can provide an aqueousdispersion which has improved dispersion stability for a wide variety ofsolids such as pigments, dyes, and so on, causes no problems such asprecipitation of the solid particles during the storage of thedispersion, and thus can be stably stored for a long time, since thedispersion of the present invention contains fine particles of awater-insoluble solid which are coated with a resin having a polyetherstructure, and the coated amount of the resin is 15 to 1,000 parts byweight per 100 parts of the solid. When a pigment is used as the abovesolid, the present invention can provide an aqueous dispersion used asan ink-jet printing ink, which has good high speed printing properties.

1. An aqueous dispersion containing a water-insoluble solid, wherein thesolid consists of fine particles surfaces of which are coated with aresin having a polyether structure, and a coated amount of the resin is15 to 1,000 parts by weight per 100 parts of the solid.
 2. The aqueousdispersion according to claim 1, wherein said solid is a pigment.
 3. Theaqueous dispersion according to claim 1, wherein said resin having apolyether structure has an acid value of 5 to 70 KOH-mg/mg.
 4. Theaqueous dispersion according to claim 1, wherein said polyesterstructure comprises at least one of a polyoxyethylene structure and apolyoxypropylene structure.
 5. The aqueous dispersion according to claim1, wherein said resin having a polyether structure comprises an acrylicresin having a polyether structure in grafted portions.
 6. The aqueousdispersion according to claim 1, wherein said resin having a polyetherstructure has a number average molecular weight of 1,000 to 100,000. 7.The aqueous dispersion according to claim 1, wherein said fine particleshas an average particle size of 0.01 to 0.3 μm.
 8. The aqueousdispersion according to claim 1, which has a surface tension of 3.0×10⁻⁴to 6.0×10⁻⁴ N/cm at a solid concentration of 3 to 10% by weight.
 9. Amethod for preparing an aqueous dispersion as claimed in any one ofclaims 1 to 8, comprising a step of mixing an organic phase containing awater-insoluble solid and a resin having a polyether structure with anaqueous phase to obtain the aqueous dispersion.